The invention relates to a method for carrying out an MRI (magnetic resonance imaging) or MRS (magnetic resonance spectroscopy) experiment on hyperpolarizable magnetic nuclei of substrate molecules and/or their metabolites contained in a living human or animal body.
NMR (nuclear magnetic resonance) techniques may be applied to gather information about a sample or sample area in a gentle, non-destructive way; in particular, clinical investigations on living patients can be done non-invasively.
However, NMR techniques are generally limited by a low sensitivity, i.e. low signal intensities. In order to improve the sensitivity, NMR experiments are performed in a static magnetic fields of high field strength such as of 1.5 T and above. Such fields are generated by superconducting magnets.
Further, the sensitivity may be increased by applying hyperpolarization techniques. Here, nuclei in a sample are prepared with a polarization level higher than corresponding to the Boltzmann distribution at the sample's temperature and the prevailing magnetic field strength, and the hyperpolarized nuclei undergo the NMR experiment. A common hyperpolarization technique is dissolution dynamic nuclear polarization (dissolution DNP), see e.g. U.S. Pat. No. 6,466,814 B1. A particularly promising hyperpolarization technique is NH-PHIP (non-hydrogenating para-hydrogen induced polarization), compare WO 2008/155093 A1.
The preparation of a hyperpolarized sample typically occurs outside the magnet used for an NMR experiment. Accordingly, the hyperpolarized sample has to be transported to said magnet, and this delay will lead to a loss of magnetization through relaxation.
Relaxation is a particularly severe problem in in vivo NMR experiments, in particular in NMR imaging. Here, time is needed to allow the hyperpolarized nuclei to migrate to the area of interest, e.g. via the blood stream, and possibly to allow a metabolic process to evolve.
In U.S. Pat. No. 7,474,095 B2 it has been proposed to prepare a sample with molecules polarized in a long-lived singlet or pseudo singlet state, and to convert this state into observable magnetization before an NMR measurement. Franzoni et al. [4] showed that long lived 1H singlet spin states originating from parahydrogen could be stored for minutes in a high magnetic field of about 7 T, and converted into triplet states by level anticrossing, involving changing the sample position to a low field area of about 0.1 T.
It is the object of the invention to provide a method for carrying out an MRI or MRS experiment which is well applicable to hyperpolarized nuclei within a living human or animal body, with reduced losses of magnetization due to relaxation processes.